1. Field of the Invention
The present invention relates to a disconnection detecting device being capable for applying to a rotating electrical machine driven by alternating current, and method being capable for detecting disconnecting of the rotating electrical machine.
2. Description of the Related Art
As this type of device, as shown in Japanese registered patent JP-B-3801471, a device that detects disconnection of a power supply line of a brushless direct-current (DC) motor is known. Specifically, predetermined conditions including a condition that the current value of at least one phase of the alternating current supplied to the DC motor is approximately zero amperes are defined. When it is judged that the predetermined conditions are continuously satisfied for a specified amount of time, the device determines that disconnection of the power supply line has occurred.
The specified amount of time is set to prevent erroneous detection of disconnection. In other words, zero-crossing of the current flowing to the DC motor occurs even when disconnection of the power supply line has not occurred. Therefore, it is required that one differentiates a fact that the current zero-crosses during a normal operation in which disconnection has not occurred and another fact that the current becomes zero amperes when disconnection has actually occurred. The specified amount of time is set so as to meet this requirement.
As the rotation speed of the DC motor becomes higher, the amount of time that the current flowing to the DC motor during normal operation becomes near zero amperes becomes shorter. Therefore, the specified amount of time is set to be relatively long time corresponding in the low-speed range in order to prevent disconnection being erroneously detected despite a disconnection not having actually occurred within the low-speed range of the DC motor. When the specified amount of time is set in this way, within the high-speed range of the DC motor, the amount of time from when a disconnection actually occurs until the disconnection is detected increases. In other words, the rotation speed range of the DC motor in which disconnection can be promptly detected may be limited.
For the purpose of preventing such situations, for example, it can be considered that setting the specified amount of time so as to become shorter as the rotation speed of the DC motor increases. However, in this instance as well, the specified amount of time cannot be shortened within the low-speed range of the DC motor. The amount of time from when a disconnection actually occurs until the disconnection is detected may become long.
Hence, a disconnection detecting device being capable of applying a rotating electrical machine and promptly detecting a disconnection is desired.